Activation volume of plastic deformation of ultrafine-grained copper

Tensile and stress relaxation tests in the temperature range 77 - 295 K were carried out to study the mechanical properties and kinetics of plastic deformation of ultrafine-grained (UFG) copper prepared by equal-channel angular hydroextrusion. The temperature and strainrate sensitivities of flow stress were analyzed to identify main mechanisms of plastic deformation. It was shown that as temperature increases the flow stress decreases but the activation volume changes non-monotonously reaching the peak value at about 200 K. In contrast to conventional copper polycrystals both temperature dependencies for UFG copper can be explained in terms of two mechanisms of thermally activated plastic deformation: ''forest'' intersection and dynamic recovery. The latter mechanism is necessary to take into account for a correct estimation of activation volume from stress relaxation tests even at low temperatures. (author)